The present invention relates to a method for forming a composite vapor-deposited film having a varied film composition at initial and final stages of vapor deposition by means of continuous vacuum vapor deposition and to a composite vapor-deposition material suitable for use in vacuum vapor-deposition therefor. In particular, the present invention relates to a method for forming a composite vapor-deposited film which has a highly varied film composition as in a reflection film and a light-absorption film attached on fluorescent material of a cathode ray tube like a color television picture tube and to a composite vapor-deposition material suitable for use in vacuum deposition therefor.
There is a need for obtaining a vapor-deposited film having plural laminated layers with different properties by means of a continuous vacuum vapor deposition process. In a cathode ray tube like a color television picture tube, for example, the inner surface of its face plate is coated with three-color fluorescent materials in the shape of dots or stripes, and a thin film layer having a high light-reflectance like aluminum is formed on this fluorescent material at the side opposite to the face plate, so that the aluminum thin film layer reflects light running inside the CRT of the visible light emitted from the fluorescent material and plays a role of increasing the amount of the light running through the face plate. In addition, on the backside of the fluorescent screen, a shadow mask or aperture grille is positioned which is a color selecting electrode to control the landing position of the electron beam on the fluorescent screen. This electrode transmits about 20% of the electron beam from the electron gun to the side of the fluorescent screen, and shields the remaining, about 80% of the electron beam. This about 80% of the electron beam will contribute to an increase in the temperature of the color selecting electrode. As the temperature increases, heat radiation from the color selecting electrode takes place, and this heat radiation converges on the closest fluorescent screen, so that most of the heat radiation is reflected by the aluminum thin film layer on the fluorescent screen. The reflected heat reaches the color selecting electrode again, and thus raises the electrode temperature to a greater extent. As the temperature rises, the color selecting electrode will undergo thermal expansion, causing its deformation. Consequently, it will be likely to result in mismatching the electron beam.
As described in U.S. Pat. No. 3,703,401, the surface of the aluminum thin film layer attached on the fluorescent screen is coated with a carbon coating, such that radiant heat from the color selecting electrode is absorbed by the heat absorption effect of the carbon coating. However, such a carbon coating must be dissolved in a solvent such as an organic solvent and the like to spray it for coating, and furthermore, it is necessary to carry out this coating step separately from a vapor deposition process of aluminum onto the fluorescent screen. Accordingly, these make not only the step troublesome, but also its continuous operation impossible.
When carbon or nickel with a property of absorbing heat rays and aluminum with a high light-reflectance are vaporized simultaneously in vacuum, it is possible to obtain a composite vapor-deposited film having an aluminum-rich composition at the initial stage of the vapor deposition and a carbon- or nickel-rich composition at the final stage of the vapor deposition, since the vapor pressure of aluminum is different from that of carbon and nickel. The aluminum-rich composition formed at the initial stage of the vapor deposition, however, contains large amounts of carbon or nickel, causing a decreased reflectance. Also, the carbon- or nickel-rich composition formed at the final stage contains large amounts of aluminum, and thus the property of absorbing heat rays cannot be satisfactory.
On the other hand, it is possible to form a vapor-deposited film of a two-layer structure having a fully different composition by loading the initial vapor-deposition material, aluminum, on a vacuum depositing tray to form a vapor-deposited film, followed by loading a vapor-deposition material different from the initial vapor-deposition material, such as carbon or nickel, on the vacuum depositing tray to carry out vapor deposition. However, this process requires two vapor deposition operations.
Deposition of chromium or iron having a property of absorbing heat rays is also carried out after the vacuum vapor depositing of aluminum having a high light-reflectance. In the composite vapor-deposited film having a layer of chromium or iron deposited on the aluminum layer, when heated to several hundred degrees centigrade after the vapor deposition, the chromium or iron may be diffused within the composite vapor-deposited film, resulting in mixing of the chromium or iron into the aluminum and a reduced light-reflectance of the aluminum layer. This leads to decreasing the brightness of a CRT.
Therefore, an object of the present invention is to provide a method for forming a composite vapor-deposited film capable of obtaining a CRT with superior brightness by means of continuous vacuum vapor deposition.
Another object of the present invention is to provide a composite vapor-deposition material and a method for producing the same which allows vapor deposition of an aluminum layer having high light-reflectance at an initial stage of the vapor deposition and subsequent, continuous vacuum vapor deposition of a layer having a property of absorbing heat rays, and at the same time, is suitable for forming a composite vapor-deposited film whose composition is not varied, even if receiving a heat history thereafter.
A further other object of the present invention is to provide a composite vapor-deposition material and a method for producing the same which is capable of enhancing brightness of a CRT by vapor depositing a layer of aluminum having high light-reflectance at an initial stage of the vapor deposition, and then continuously vacuum vapor depositing over the layer a layer having a tendency of transmitting a electron beam and a property of absorbing heat rays.
Therefore, a method for forming a composite vapor-deposited film according to the present invention which is capable of making a CRT with superior brightness by continuous vacuum vapor deposition comprises heating under reduced pressure a composite vapor-deposition material having an aluminum body and powder of a low vapor-pressure metal/metalloid compound retained in a core region of the aluminum body, vaporizing aluminum and low vapor-pressure metal/metalloid compound in series, and vapor depositing them on a substrate to be deposited.
In the specification, when materials of different types are heated under the same vacuum, a material which vaporizes at a low temperature is defined as a high vapor-pressure material, and a material which vaporizes at an elevated temperature is defined as a low vapor-pressure material. In the present invention, aluminum is utilized as a high vapor-pressure material. A metal/metalloid compound, for example, an oxide, carbide, and nitride, vaporizes at higher temperatures than aluminum, and are sometimes referred to as a low vapor-pressure material or low vapor-pressure metal/metalloid compound.
The above-mentioned low vapor-pressure metal/metalloid compound is of powder, and a composite vapor-deposition material having a structure in which such powder is dispersed and retained with aluminum in the core region of the aluminum body can be utilized to form a composite vapor-deposited film by continuous vacuum vapor deposition. As low vapor-pressure metal/metalloid compound powder can be employed an oxide, nitride, carbide, silicide, nitro-oxide, carbo-nitride, carbo-oxide, silico-oxide, silico-nitride, or boride of a metal/metalloid element. As a metal/metalloid element, at least one element can be selected from the group consisting of Li, Be, Mg, Ca, Ti, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, B, Al, C, Si, Sn, and Pb. Among these metal/metalloid elements, an element having an atomic number of 20 or less (at least one element selected from the group consisting of Li, Be, B, C, Mg, Al, Si, and Ca) is preferable, since such a element has a low level of absorbing the electron beam, so that the brightness of a CRT can be increased even in the case where the same accelerating voltage is applied. Preferable low vapor-pressure metal/metalloid compounds are nickel oxide, iron oxide, silicon carbide, aluminum nitride, boron nitride, and magnesium boride.
This composite vapor-deposition material can possess a foil or layer of a metal having a further lower vapor pressure, preferably tantalum, rhenium, tungsten, molybdenum, or the like, which surrounds the core region.
The composite vapor-deposition material of the present invention can take a composite structure in which powder of a low vapor-pressure metal/metalloid compound is dispersed and retained with aluminum in the core region of an aluminum body by integrally cold working an aluminum envelop with a hollow inside and a mixture of aluminum powder and powder of a low vapor-pressure metal/metalloid compound which is filled in the hollow.
It is preferable that the low vapor-pressure metal/metalloid compound powder has a particle size of not more than 3 xcexcm for 70% or more of the number of particles. It is desirable that the average particle size of the low vapor-pressure metal/metalloid compound powder is between 0.05 xcexcm and 4 xcexcm, and preferably between 0.05 xcexcm and 2 xcexcm. It is preferable that the core region of the aluminum body has an apparent specific gravity of 40% to 90% of the true specific gravity.
The method for producing a composite vapor-deposition material according to the present invention comprises the steps of mixing aluminum powder and powder of a metal/metalloid compound having a vapor pressure lower than that of aluminum, filling the mixed powder into an aluminum envelope, and subjecting the envelope to cold working to reduce the diameter thereof, thereby forming a composite structure in which the low vapor-pressure metal/metalloid compound powder is dispersed in the core region of the envelope. Preferably, the above-mentioned cold working is done as cold wire drawing. It is preferable that the total reduction rate is 75% or higher in the cold wire drawing. It is preferable that the mixed powder has an angle of repose of not more than 60 degrees, and preferably not more than 45 degrees.
In the method for producing a composite vapor-deposition material according to the present invention, it is also possible to cut and remove an end region including the closed portion of wire-drawn aluminum envelopes, and to connect them at their cut portions by welding, followed by further cold wire drawing.